This invention relates generally to a packaging arrangement for an energy dissipating device, such as an electronic component, and more specifically to a unitized packaging arrangement which utilizes preformed thermoplastic components.
Traditional packaging arrangements for electronic components include dual in-line packages (DIP's), single in-line packages (SIP's), small outlines (SO's) and the leaded chip carrier family. These traditional packaging arrangements are based on the use of metallic leadframes having plurality of leads which are interconnected on one end to the bonding pads of the device and which extend through the package to provide a means for connecting the device to external components. Maintaining an adequate seal between the leads of the leadframe and the packaging material used to encapsulate the leads and the device has been a source of concern in the electronics packaging industry. These concerns are discussed in my co-pending patent application entitled "Packaging Arrangement For Energy Dissipating Devices" filed on Jan. 20, 1987, and assigned Ser. No. 004,70, and a continuation in-part of that application, entitled "Preformed Packaging Arrangement for Energy Dissipating Devices," filed concurrently with the present application and assigned Ser. No. 75,642. To the extent necessary to further the understanding of the present invention, the disclosures of those applications are hereby incorporated into the present application by reference thereto.
An alternative approach to the above-mentioned packaging arrangements is the pin grid array (PGA) family of packages in which a plurality of conductor pins are arranged in an array rather than in single or double lines, squires or other configurations. The pins extend through the enclosure surrounding the device, and are normally intended to extend through holes in a printed circuit board or otherwise mate with known forms of interconnecting devices. For the most part, the PGA packaging format is not readily compatible with the emerging trend toward the use of surface mounted components on printed circuit board assemblies.
An object of the present invention is to provide a unified approach to the design of packaging arrangements for electronic devices, which arrangements are compatible or interchangeable with known arrangements, such as DIP's, SIP's, QUAD's and PGA's.
Another object of the present invention is to provide a packaging arrangement for an energy dissipating device which is especially well suited for the surface mounting of devices on printed circuit boards.
Yet another object of the present invention is to provide a packaging arrangement for an energy dissipating device which utilizes injection molding and metallization techniques in its construction.
A still further object of the present invention is to provide a packaging arrangement for an energy dissipating device which provides optimal protection for the device against the ingress of moisture into the packaging arrangement.
Yet still another object of the present invention is to provide a packaging arrangement for an energy dissipating device which may be readily and efficiently assembled by automated techniques.
These and other objects of the invention are attained in a packaging arrangement which includes a thermoplastic housing which is especially formed to mountably receive an energy dissipating device, and which is provided with a pattern of electrical conductors deposited on an outer surface thereof. The conductor pattern is connected to the bonding pads of the device. A preformed thermoplastic base is formed to mountably receive the thermoplastic housing and is provided with means (such as a plurality of openings) for providing access to the electrically conductive pattern from outside the packaging arrangement. The arrangement further comprises a preformed thermoplastic cap, and means for joining the thermoplastic housing, the thermoplastic base, and the thermoplastic cap to form the unitized packaging arrangement for the device. The electrically conductive pattern preferably includes a plurality of openings formed in the thermoplastic housing. At least a portion of the surface of the openings is preferably metallized. In an especially preferred embodiment, conductive elements, in the form of conductive pins, are located within the openings. The conductive elements are preferably joined to the metallized surface of the openings by a reflow soldering technique.
In the preferred embodiment of the packaging arrangement of the present invention, at least a portion of the interior surfaces of the preformed thermoplastic base and cap, and a matching portion of the exterior surface of the thermoplastic housing, are also metallized. The metallized areas are pre-tinned prior to assembly of the base, housing and cap, so that these elements may be mechanically joined together by reflow soldering. In addition to providing the mechanical means for holding these elements together, the metallized layers provide a barrier against the ingress of moisture into the interior of the packaging arrangement where the device is located. For this reason, the metallization preferably extends to substantially all of the interior surfaces of the base and cap, and exterior surfaces of the thermoplastic housing. This arrangement further provides a degree of electromagnetic shielding of the device and, thus, decreases electromagnetic interference and possibly increases the radiation hardness of the device.
In the preferred embodiment of the invention, special care is taken to electrically isolate the electrically conductive elements which are connected to the bonding pads of the device from the metallized interior and exterior surfaces of the base, cap and housing. These metallized surfaces may, however, be intentionally placed in thermal communication with the device in order to regulate heat transport from the device.
The preferred method of constructing the packaging arrangement of the present invention includes the steps of: forming the thermoplastic housing; depositing conductor means on a surface of the housing; mounting the energy dissipating device in the housing; connecting the bonding pads of the device to the conductor means; forming a thermoplastic cap and base; and joining the thermoplastic housing, base, and cap to form a unitized packaging arrangement for the device. An especially preferred method of the present invention further includes the additional steps of: metallizing at least a portion of an exterior surface of the thermoplastic housing; metallizing at least a portion of respective interior surfaces of the thermoplastic cap and base; and joining the thermoplastic housing, base and cap by a metal-to-metal bonding technique, such as soldering.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.